1. Field of the Invention
The present invention relates to an electric shaver, more particularly, to control of a motor which is a core of its driving mechanism and detection of the load state thereof.
2. Description of the Related Art
In an electric shaver, by cooperative operations between an outer cutter which induces and leads in beards and an inner cutter which is driven by a motor, the beards induced by the outer cutter are cut.
With respect to control of a motor incorporated in such an electric shaver, for example, U.S. Pat. No. 4,594,777, Japanese Patent Application Laid-Open No. 62-79084 (1987) and so on are given as the prior arts.
In the former, a plurality of diodes are connected in series to a serial circuit of a battery and the motor, and by selecting how many diodes to be by-passed by mechanical switching means the applied voltage to the motor is adjusted to control the motor speed.
In the latter, the magnetic flux of the motor is detected by a Hall device, and the applied voltage to the motor is decided in response to the result of keeping the rotational speed of the motor at constant. This is for keeping the motor at its optimum rotational speed of 7000 r.p.m. such that the motor speed will not drop even in the case of thick beards.
However, since the motor is driven at constant speed for both a person having thick beards and a person having thin beards, the motor speed is so fast for the latter that the beards are not sufficiently induced into a cutter unit or twitches apt to occur. In the case where of the person having thick beards, since the motor is kept at constant speed during shaving, there is the possibility that, as same as stated above, the beards are not sufficiently induced or twitches may occur as the shaving proceeds. Thus, it is desirable to control the motor speed which is suitably responsive to thickness of the beards.
Meanwhile, refuses of the beards induced by the outer cutter and cut by the inner cutter are stuck to the inner cutter or dropped into a receptacle of the inner cutter and cumulated therein. Where the refuses are cumulated in the receptacle of the inner cutter, they are scattered to the outside or produce a bad smell and give an unpleasant feeling to the user. Moreover, by the refuses stuck to the inner cutter, whose, cutting performance is deteriorated or loads of the motor increase to damage the cutter, or the power consumption increases to deteriorate the battery life rapidly. Therefore, though it is desirable to clean the refuses by blushes or the like every time after shaving, it is very troublesome and annoying for the user, since, generally, the outer cutter must be removed from the body itself. When neglecting the cleaning of refuses, they are excessively cumulated to cause discomfort to the user as aforementioned.